1. Field of the Invention
This invention is directed to a method for the treatment of dredged material. More particularly, this invention is directed to a method to decontaminate and solidify dredged material so as to render it suitable for beneficial use.
2. Background Information
Harbors and waterways require shipping lanes to be dredged on a regular maintenance basis in order to prevent the shipping lanes from silting up. Material that is dredged out of port or harbor locations typically contains a wide range of toxic contaminants, from heavy metals to oils and pesticides. Three alternatives may be considered for management of dredged material: confined disposal, open-water disposal, and beneficial use.
Confined disposal is problematic since confined facilities must have all potential escape routes of the contaminants eliminated, including effluents during placement, surface runoff, leachates, direct uptake by plants and animals and volatilization to air. Open-water disposal is limited by the fact that the dumping of contaminated sediments in waters is not permitted under various legislative measures, including, for example, the Marine Protection, Research, and Sanctuaries Act. Accordingly, treatment of the contaminated dredged material for rendering it suitable for beneficial use is a most desirable alternative.
Several examples of beneficial use are available. For example, the dredged material may be used as beach nourishment, which may be necessary if natural replacement of material moved along the shoreline by littoral transport is not available. However, only the gravel and sand portion of dredged material is suitable for beach nourishment, making separation and decontamination obligatory. As a second example, dredged material may be used as manufactured topsoil; however, only fine particles are suitable for such use, so that separation and decontamination of clay and silt is required. In addition, when used for agricultural purposes, the material has to be suitably clean and must not contain excessive amounts of salts, which can make the material unusable for growth of most plants. A more promising beneficial use for dredged material is as a filler for composite materials. However, such use requires not only effective decontamination but also solidification of the dredged material.
One solution to the problem of treatment of contaminated dredged material is the use of chemical substances capable of neutralizing heavy metals and other toxins, such as the chelating agents described in U.S. Pat. No. 5,714,085 (herein incorporated by reference). For example, the chelating agents of U.S. Pat. No. 5,714,085 remove heavy metals and certain organic contaminants such as polychlorinated biphenyls. These chelating agents are advantageous when compared to microorganisms, which can remove organic contaminants but cannot remove heavy metals and other inorganic contaminants. However, the chelating agents of U.S. Pat. No. 5,714,085 were developed only for decontamination, and not for solidification as well. Solidification of the dredged material is necessary to make it suitable as a filler for composite materials such as concrete.
None of the prior art, including U.S. Pat. No. 5,714,085, provides a commercially viable method that results both in decontamination and in solidification of the dredged material that renders the material suitable as a filler for composite materials.